It should be noted that, not only the methodology for designing an unconventional measurement, the research for finding a suitable optical light also has been performed[1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}. In this topic, the main purpose was to investigate how much the Helstrom bound can be improved by changing the form of an (ideal or noisy) optical state. For example, the Helstrom bound is known to be improved by squeezing operation on a coherent state[8]}. Likewise, a phase-diffused coherent state[3]}, a thermal optical state[4]}, and a single rail qubit[5]} were considered as an information carrier. Recently, it was shown that the generalization of binary coherent states can increase the Helstrom bound[7]}. This result implies that the non-standard coherent state (NS-CS) can enhance the capability of quantum communication. Especially, if binary (modified) Susskind-Glogower coherent states (mSG-CS) are considered [13]}, Helstrom bound can be equal to one without large mean photon number. Therefore, concerning binary coherent states, finding the optimal structure of the unconventional measurement is important for implenting the enhanced quantum communication.
